IF you’re looking for an uplifting movie, “Trade” isn’t it. With Kevin Kline starring as a cop who helps a Mexican boy (Cesar Ramos) track down his kidnapped 13-year-old sister (Paulina Gaitan), the film, opening Sept. 25, explores the dark underbelly of sex trafficking, which is suddenly finding traction in Hollywood. It also figures into the plot of the recently released “Eastern Promises” and the upcoming “Holly,” which focuses on Thailand.

German director Marco Kreuzpaintner says making “Trade” was a “big lesson in how trafficking works.” We asked him to share the five most startling facts he learned about the business.

1Humans are being sold online. “With the help of the FBI, I was allowed to go to some of those auction pages, and I learned that this works like a human eBay,” Kreuzpaintner says. “It was so shocking. It wasn’t that there was nudity. It was more done totally as if someone was talking about goods: the sizes of the girls, the weight, the color. You had a feeling that this was the most disturbing thing that capitalism ever brought.”

2Seemingly law-abiding people are participating. Buying one of these girls can cost as much as $50,000 – an enormous amount of money that only a few wealthy people can afford to pay. “We’re talking about people among us, not anti-social people, ex-prisoners or people we look down on. We’re talking about people in our own back yard,” Kreuzpaintner says.

3Traffickers are patient and cunning. “They are choosing their victims very carefully. They’ve watched them. It’s not like they just grab them,” he says. By spying on potential victims, traffickers learn about their friends and family. Threatening loved ones is a common tactic the criminals use to keep the girls from running away. The traffickers also pluck victims from particular regions.

“They go mostly into Catholic places,” he says. “With the upbringing of those kids and the whole sexual morals, even if those kids could run away from the holders, most of the time they are so ashamed and so scared to go back because they have the feeling they won’t be welcome. They feel dirty.”

4Business is booming. “Worldwide, 12 million people are enslaved. I’m not talking about just sex trafficking, but 12 million people are enslaved. That’s more than ever, ever, in history, including the time of slavery in the United States,” he says.

5Dealing cinematically with the issue wasn’t easy. “You have to, as a filmmaker, avoid making these people a victim for a second time,” he says. To the director that meant having some of the kidnapped characters in the film fight against their captors and a implementing a strict no-nudity policy. “I wanted to avoid anyone in the movie theater getting excited by seeing those kids,” he says.